Generally, interlayer connection is achieved in a substrate by performing copper plating. For example, as shown in FIG. 19, in an insulative substrate 300, a surface layer 301 (e.g., copper foil) and a surface layer 302 (e.g., copper foil) are connected by a copper plating layer 304 formed on an inner wall surface of a through hole 303. When the interlayer connection was performed with such typical copper plating, a large current (e.g., 120 amperes) cannot flow to the copper plating layer 304.
Patent document 1 discloses technology that allows for the flow of a large current. More specifically, in a printed wiring board, current through holes, which extend from a front side to a rear side of a substrate, are arranged in a concentrated manner. This allows for the flow of a large current of 50 to 180 amperes without using a bus bar.